Hardbanding is a surface welding process that is commonly used in the oil and gas industry to apply metal welding wire onto the surface of many industrial parts, including tool joints of drill pipe. In such a process an elongated metal wire is welded to the tool joint to build, reinforce, or repair the part to extend the utility of the part that is subjected to high frictional forces and abrasive forces. In oil drilling applications for the oil and gas industry, for example, drill pipes are connected together at the ends which are referred to as “tool joints” to form a “drill string” of several hundred feet lengths. The tool joints have a much larger outside diameter than the tube portion of the drill pipe, and therefore, the vast majority of the wear during drilling occurs on the tool joints. To protect the tool joints from excessive wear they are surfaced welded with an appropriate abrasion resistant consumable welding wire. The inside of the drill pipe is coated with a polymer, an internal polymer coating (IPC), to protect against corrosion by the fluid or particles entrained in the fluid during drilling.
Typically the initial hardbanding of drill pipe usually occurs at the drill pipe manufacturer's facility. Tool joints of drill pipe in the oil and gas industry are applied as a “weave bead” weld deposits of about one inch (1″) wide. The heat produced by the welding during hardbanding melts the base metal of the tool joint beneath the surface in the area where the welding wire is applied. During the subsequent cooling process a portion of the base metal beneath the welding arc forms a low hardness metallurgical phase which is referred to as the base metal “heat affected zone” (HAZ) or base metal HAZ. Once the hardbanding process is complete, the internal plastic coating (IPC) is applied to the inside surface area of the drill pipe. The finished drill pipe is then shipped to the drill site and put into service until it must be undergo another hardbanding process due to wear of the hardbanding material, or other anomalies, during drilling.
The known methods of the re-application of hardbanding on worn tool joints presents technical challenges in maintaining properties required industry standards. Conventional processes for the re-application of hardbanding includes preheating the tool joint from 250° F. to 600° F., welding with the wire to the worn surface of the previously applied hardbanding, followed by slow cooling. The high preheating and welding temperatures cause the internal polymer coating on the inside surface of the tool joint to deteriorate during welding. For many drilling environments, this degradation of the polymer coating is unacceptable and so the drill pipe requires an additional coating process after reapplication of the hardbanding. An alternative hardbanding process to preserve the internal polymer coating is to introduce standing or continuously running water through the inside diameter of the pipe during the welding process. While this procedure can maintain the properties of the polymer coating, water cooling effectively quenches the weld deposit and hardens the base material HAZ to Rockwell hardness greater than the maximum industry specification of 40 Rc. Thus, the current known methods for reapplication of hardbanding, whether or not water is employed, results in rejected tool joints and drill pipes.